title: Thyroid hormone-induced changes in the hepatic monooxygenase system, heme oxygenase activity and epoxide hydrolase activity in adult male, female and immature rats.
abstract: In 8-day-old rat pups, pretreatment with a single injection of L-triiodothyronine or L-thyroxine decreased hepatic cytochrome P-450 content, aminopyrine N-demethylase activity and epoxide hydrolase activity but increased hepatic microsomal cytochrome c reductase, 7-ethoxyresorufin O-deethylase and heme oxygenase activities without significantly altering UDP-glucuronosyltransferase activity (towards o-aminophenol) or the microsomal yield. In adult rats of either sex such single injections of L-triiodothyronine failed to significantly alter these enzyme activities. However, multiple injections evoked changes similar to those observed in the pups, in all these enzyme activities, except that 7-ethoxyresorufin O-deethylase activity was slightly decreased rather than increased. These findings demonstrate that: (1) The hepatic monooxygenase system in the rat pup is more responsive to thyroid hormones than that in adult. (2) Thyroid hormones can decrease rat liver cytochrome P-450 content and its dependent monooxygenase activity independently of sexual maturity. (3) Thyroid hormones also decrease hepatic epoxide hydrolase activity in both pups and adults. Thus, hyperthyroidism could render the rat pup more susceptible to hepatotoxicity from electrophilic epoxides which utilize microsomal epoxide hydrolase as the major detoxication pathway.
mesh_terms: D000633:Aminopyrine N-Demethylase / Q000378:metabolism; D000818:Animals; D019363:Cytochrome P-450 CYP1A1; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology; D004851:Epoxide Hydrolases / Q000378:metabolism*; D005260:Female; D014453:Glucuronosyltransferase / Q000378:metabolism; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D008297:Male; D006899:Mixed Function Oxygenases / Q000378:metabolism*; D009245:NADH Dehydrogenase / Q000378:metabolism; D010088:Oxidoreductases / Q000378:metabolism; D051381:Rats; D012727:Sex Characteristics; D012741:Sexual Maturation; D013963:Thyroid Hormones / Q000494:pharmacology*; D013974:Thyroxine / Q000494:pharmacology; D014284:Triiodothyronine / Q000494:pharmacology
chemical_list: D013963:Thyroid Hormones; D014284:Triiodothyronine; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D010088:Oxidoreductases; D019363:Cytochrome P-450 CYP1A1; D006419:Heme Oxygenase (Decyclizing); D000633:Aminopyrine N-Demethylase; D009245:NADH Dehydrogenase; D014453:Glucuronosyltransferase; D004851:Epoxide Hydrolases; D013974:Thyroxine